State-of-the-art Vertical Cavity Surface Emitting Lasers (VCSELs) have an oxidized high-Al containing layer to form a current aperture to confine carriers and photons. Mesa etching is needed to expose the aperture layer to the lateral oxidation process which has the side-effect that also other layers such as Distributed Bragg Reflector layers (DBRs) are exposed to the oxidation process. It is important that the parasitic oxidation rate of the DBR layers is slower than the aperture layer which limits the high-Al fraction in the DBRs to ˜90% for practical use.
US 2010/0226402 A1 discloses a laser diode including a laminate configuration including a lower multilayer reflecting mirror, an active layer and an upper multilayer reflecting mirror in order from a substrate side, in which the laminate configuration includes a columnar mesa section including an upper part of the lower multilayer reflecting mirror, the active layer and the upper multilayer reflecting mirror, and the lower multilayer reflecting mirror includes a plurality of pairs of a low refractive index layer and a high refractive index layer, and a plurality of oxidation layers nonuniformly distributed in a direction rotating around a central axis of the mesa section in a region except for a central region of one or more of the low refractive index layers.
EP 0 905 835 A1 discloses an independently addressable, high density, vertical cavity surface emitting laser/LED structure formed by a lateral oxidation process. The aperture of the laser structure is formed by either lateral wet oxidation or by both selective layer intermixing and lateral wet oxidation from a semi-annular groove etched in the laser structure.